Taxanes, which are an anticancer agent showing their anti-proliferative effect by acting on the organization of the microtubules in the cellular cytoskeletal system (Huizing M. T. et al., Cancer Inv., 1995, 13: 381-404), are known to exhibit excellent cytotoxicity against various kinds of cancers such as ovarian cancer, breast cancer, esophagus cancer, melanoma and leukemia. Parenteral dosage forms of paclitaxel and docetaxel are commercially available under the trademarks Taxol™ and Taxotere™, respectively. Since a taxane is known to have very low water solubility, the currently available paclitaxel-containing formulation, e.g., Taxol™, has been formulated into the form of emulsion preconcentrate, which is diluted before using for injection. However, in order to overcome the problems related to patient compliance due to the use of the injection form, stability of the formulation, and safety to the human body, etc., researches on the formulations for oral administration are being carried out.
Meanwhile, it has been reported that the oral administration of a taxane such as paclitaxel exhibits very low oral bioavailability due to the action of an outwardly directed efflux pump (Walle et al, Drug Metabo. Disp. 26(4): 343-346 (1998)). It has been also reported that the orally administered paclitaxel is very poorly absorbed (less than 1%) (Eiseman et al, Second NCI Workshop on Taxol and Taxus (sept. 1992), Suffness (ed.) et al, Taxol™ Science and Applications, CRC Press (1995)). As an attempt to improve such a low oral bioavailability, Korean Patent Publication No. 10-2004-0009015 has disclosed a solubilized taxane-containing composition for oral administration, which is formulated by using a medium chain triglyceride such as triacetin, a monoglyceride such as monoolein, and a surfactant such as Tween. Said composition is a solubilized taxane-containing composition for oral administration, whose bioavailability is increased through high mucoadhesive property in the intestine by the monoglyceride such as monoolein. And also, Korean Patent Publication No. 10-2007-0058776 has disclosed an improved process for preparing the solubilized taxane-containing composition for oral administration, the process comprising dissolving paclitaxel, along with a medium chain triglyceride, a monoglyceride, and surfactant, in an organic solvent.
Solid formulations such as soft capsules have advantages in terms of the ease of use, compared to the lipid solution form. Considering the patient's compliance, it is necessary to control the size of the soft capsules to an appropriate size. Therefore, in order to prepare a soft capsule containing the therapeutically effective amount of a taxane, it is required to prepare a lipid solution containing the taxane in a high concentration. However, when a taxane is contained in a high concentration (for example, 4% by weight or more) according to conventional formulation methods (e.g., Korean Patent Publication Nos. 10-2004-0009015 and 10-2007-0058776), the taxane is precipitated from the lipid solution and thus the completely solubilized lipid solution cannot be obtained, thereby leading to the problem of decreased bioavailability.